Natural gas is a vital component of the world's supplies of energy. It is one of the cleanest, safest, and most useful energy sources. Natural gas is combustible, and when burned, it gives off a large amount of energy. However, unlike other fossil fuels, natural gas burns cleanly and emits lower levels of potentially harmful by-products into the air.
Typically, natural gas is a combustible mixture of hydrocarbon gases. While natural gas is formed primarily of methane, it can also include ethane, propane, butane and pentane. The composition of natural gas can vary widely. Once brought from underground, natural gas is refined to remove impurities like water, other gases, sand, and other compounds. Some hydrocarbons may be removed and sold separately, including propane and butane for liquefied petroleum gas (LPG) production. After refining, the clean natural gas is transmitted through a network of pipelines. From these pipelines, natural gas is delivered to its point of use.
Worldwide, natural gas is used for many residential, commercial, and industrial applications. Residential applications typically use natural gas for heating and cooling homes, heating water, and fuelling gas ranges. Commercial applications, such as grocery stores and office buildings, use natural gas for e.g. heating and cooling. For industrial applications, natural gas is used e.g. as a feedstock for making chemicals such as anhydrous ammonia, and as a fuel for boilers and furnaces which may, in turns, generate electricity.
As mentioned above, natural gas is supplied to the customers via natural gas pipelines. This requires metering stations to be placed periodically along specific sections of the natural gas pipelines. These stations allow pipeline companies to monitor and manage the natural gas in their pipes. Essentially, these metering stations measure the flow of gas along the pipeline and calculate the amount of energy from the natural gas that is being transported via underground pipelines to the respective customers, thereby allowing pipeline companies to ‘track’ the natural gas as it flows along the pipeline. These stations usually employ specialized meters and computers to measure the natural gas as it flows through the pipeline, without causing any flow interruptions to their respective customers. Such stations are also known as custody transfer points, where the ownership of gas molecules exchanges between contractual binding parties.
Accurate delivery to the customer is crucial for any natural gas transporter company. Any unaccounted for gas (UFG) can cause significant damage to the accounting book, i.e. a loss of profit. Typically, in order to manage the natural gas that enters the pipeline, and to ensure that all customers receive accurate delivery of their respective portions of this gas, sophisticated control systems are required to monitor the gas as it travels through all sections of the lengthy pipeline network.
For example, in a conventional approach, a supervisory control and data acquisition (SCADA) system is used. Billing is generated by the flow computer and the only means of verification is through validation, which is usually carried out e.g. once every 6 months. Thus, there may be errors in calculating the energy figure which are not timely detected. Some major contributing factors include drift, malfunctioning and freezing of measuring equipment (e.g. pressure, temperature and flow transmitters) at various custody transfer points, calculation error from the flow computer that is doing the billing calculation, gas chromatograph error and validation error. Importantly, a slight error in calculating the energy figure may lead to significant loss of profit.
A need therefore exists to provide a method and system for validating an energy measurement in a gas distribution network that seek to address at least one of the above problems.